1. Field of the Invention
The present invention relates to a power generating system using a fuel cell which generates a fuel gas containing a hydrogen gas by reforming fuel such as a natural gas with steam, and generates power by reacting the fuel gas with an oxidizing gas, such as oxygen in the air, by electrochemical reaction, and an operation method for the system.
This application is based on Japanese Patent Application Nos. 2000-185355 and 2000-185356, the content of which are incorporated herein by reference.
2. Description of the Related Art
A fuel cell power generating system typically uses coolant, which adjusts the temperature inside a fuel cell stack, in order to keep the power generating efficiency of the fuel cell high. The coolant is normally subjected to demineralization before usage.
FIG. 6 exemplifies a fuel cell power generating system, which comprises a fuel cell unit 1, a water storage tank 2 for water which serves as the coolant for the fuel cell unit 1, a water treatment system 3 which performs purification of the water in the water storage tank 2 and supplies the resultant water as coolant to the fuel cell unit 1, a heat exchanger 4 for recovering the exhaust heat which heats water using the exhaust heat from the fuel cell unit 1, a hot water storage tank 5 which retains hot water obtained by using the heat exchanger 4, and a auxiliary water supply path 42 which supplies auxiliary water to the water storage tank 2.
The fuel cell unit 1 has a heat exchanger 17 for recovering the condensed water in the exhaust gas which recovers steam in the exhaust gas as condensed water.
The water treatment system 3 has water purifying equipment 19 such as an ion-exchange demineralizer, and a water feed pump P1.
The hot water storage tank 5 is constructed in such a way as to be able to feed hot water in the tank to a heat using equipment (not shown).
In the fuel cell power generating system, the fuel cell unit 1 generates a fuel gas containing a hydrogen gas by reforming fuel such as natural gas with steam and generates power by reacting the fuel gas with an oxidizing gas, such as atmospheric oxygen by electrochemical reaction, and the heat exchanger 17 condenses the steam in the exhaust gas by cooling it down, recovers the condensed water and retains it in the water storage tank 2. Auxiliary water, such as city water, is supplied into the water storage tank 2 through the auxiliary water supply path 42.
Ions (carbonate ions, metal ions or the like) or a solid material, which are originated from auxiliary water, such as city water, are fed in the water storage tank 2 as impurities, and the supply water in the water storage tank 2 is supplied to the fuel cell unit 1 as coolant after the impurities are removed by the water purifying equipment 19 of the water treatment system 3. This can prevent the occurrence of scaling or the like in a coolant circulation path.
Because a large load is applied to the water purifying equipment 19 in the fuel cell power generating system, however, the water purifying equipment 19 in use can be complex and large, thus resulting in a large increase in equipment cost. In a case where an ion-exchange demineralizer is used, for example, the operation cost, such as a regenerating cost, increases.
FIG. 7 shows another example of the fuel cell power generating system. The system comprises fuel cell power generating equipment 61 which generates power by reacting fuel gas containing a hydrogen gas with an oxidizing gas by electrochemical reaction, a hot water storage tank 52 which retains hot water heated up by using the heat generated at the time power is generated by the power generating equipment 61, and a auxiliary water supply path 69 which supplies auxiliary water, such as city water, to the hot water storage tank 52.
The fuel cell power generating equipment 61 has a fuel cell stack 53, a coolant circulation path 64 which regulates the temperature of the fuel cell stack 53, a heat exchanger 65 for recovering water which condenses and recovers steam in the exhaust gas discharged from the fuel cell stack 53, a water storage tank 56 which retains supply water recovered by the heat exchanger 65, water purifying equipment 57 which purifies the supply water in the water storage tank 56 and supplies the purified water as coolant to the coolant circulation path 64, an heat exchanger 58 which heats up and makes water hot using the coolant, and a auxiliary water supply path 70 which supplies auxiliary water, such as city water, to the water storage tank 56.
The fuel cell stack 53 is designed to have an electrolyte 73 sandwiched between a anode 71 and an cathode 72. Electrode plates 74 and 75 are respectively provided between the anode 71 and the electrolyte 73 and between the cathode 72 and the electrolyte 73.
An ion-exchange demineralizer or the like, which removes impurities from the supply water from the water storage tank 56, is used as the water purifying equipment 57.
The hot water storage tank 52 can supply hot water in the tank to heat using equipment (not shown).
The fuel cell power generating system allows a reformer (not shown) to reform fuel such as a natural gas with steam, thus generating a fuel gas containing a hydrogen gas, supplies the fuel gas to the anode 71 through a fuel-gas supply path 76, and supplies an oxidizing gas, such as air, to the cathode 72 through an oxidizing-gas supply path 77, so that the fuel gas reacts with the oxidizing gas electrochemically, thereby generating power.
The fuel-based exhaust gas from the reformer is discharged outside the system via the heat exchanger 65 through an exhaust path 78. The oxidant-based exhaust gas from the cathode 72 travels through an exhaust path 79, merges with fuel-based exhaust gas in the exhaust path 78, and is discharged outside the system via the heat exchanger 65.
As the coolant circulates in the coolant circulation path 64, the fuel cell stack 53 is cooled down to maintain the pre-set temperature. At this time, the coolant is heated to a high temperature (normally 60 to 80xc2x0 C.) and is led into the heat exchanger 58.
In the heat exchanger 58, the hot coolant heats up the water in the hot water storage tank 52 and makes it as hot as about 50 to 60xc2x0 C. The coolant that has passed through the heat exchanger 58 is led into the exchanger 65 through the path 66, and is then led into the water storage tank 56 through the path 67.
In the exchanger 65, the steam in the fuel-based exhaust gas and oxidant-based exhaust gas in the exhaust path 78 is cooled and condensed by the coolant, and the condensed water is recovered into the water storage tank 56 through the path 62. When the supply water in the water storage tank 56 becomes insufficient, auxiliary water such as city water is provided as a supplement through the auxiliary water supply path 70.
Carbonate ions or metal ions for example, originated from auxiliary water, such as city water, are fed in supply water in the water storage tank 56 as impurities, and the supply water is supplied to the coolant circulation path 64 in the fuel cell stack 53 as coolant through a supply path 63 after impurities are removed by the water purifying equipment 57. This can prevent the occurrence of scaling or the like in the coolant circulation path 64.
Because a large load is applied to the water purifying equipment 57 in the fuel cell power generating system, however, the water purifying equipment 57 in use can be complex and large, thus increasing the equipment cost. There is another problem that the operation cost, such as the regenerating cost for an ion exchange resin, increases.
Accordingly, it is an object of the present invention to provide a fuel cell power generating system and an operation method therefore, which can reduce the equipment cost and the operation cost.
To achieve the above object, according to the first aspect of the invention, there is provided a fuel cell power generating system comprising a fuel cell unit having a coolant circulation system; a water storage tank for supply water to be serve as coolant for the fuel cell unit; a water treatment system for purifying the supply water in the water storage tank and supplying the purified supply water as coolant to the fuel cell unit; heating means for heating water; a hot water storage tank for hot water acquired by the heating means; and a condensed-water supply system for supplying the water storage tank with condensed water obtaining by condensing steam from the hot water in the hot water storage tank.
As the fuel cell power generating system of the invention has the condensed-water supply system that supplies the water storage tank with condensed water obtaining by condensing steam from the hot water in the hot water storage tank, it is possible to supply condensed water or distilled water containing an impurity, such as ions or a solid material, which has a low concentration, to the water storage tank as auxiliary water, thereby reducing a load of demineralization or the like applied to the water treatment system.
It is therefore possible to set the capacity of the water treatment system low and restrain the equipment cost and the operation cost low.
The heating means may be constructed in such a way as to be able to heat water by using heat generated at the time the fuel cell unit generates power.
This structure can provide hot water by using the exhaust heat generated by the fuel cell unit, thus ensuring an improvement of the energy efficiency.
The condensed-water supply system may have a heat exchanger for condensing steam from the hot water in the hot water storage tank by cooling that steam with auxiliary water to be supplied to the hot water storage tank and recovering the condensed water, and a condensed-water supply path for supplying the condensed water recovered by said heat exchanger to the water storage tank.
This structure eliminates the need for a separate cooling medium at the time the condensed-water supply system condenses steam, thus restraining the operation cost further.
The hot water storage tank may be provided inside with a partition for defining a plurality of rooms in the hot water storage tank in such a way that the hot water heated by the heating means is led into one of the rooms and steam from the hot water in that room is supplied to the condensed-water supply system.
This structure can prevent water in the other rooms from entering the room whose steam is to be supplied to the condensed-water supply system, keep the temperature of the hot water in that room high, and increase the vapor pressure in that room.
It is therefore possible to increase the steam content in the gas that is led into the condensed-water supply system, thus improving the efficiency of recovering the condensed water.
This can increase the amount of the condensed water having a low impurity concentration to be supplied to the water storage tank, thus reducing a load of demineralization or the like applied to the water treatment system. This leads to a further reduction in equipment cost and operation cost.
The above-described fuel cell power generating system can be operated by using a method which supplies the water storage tank with condensed water obtaining by condensing steam from the hot water in the hot water storage tank.
According to the second aspect of the invention, there is provided a fuel cell power generating system comprising a fuel cell power generating equipment for generating power by reacting a fuel gas containing a hydrogen gas with an oxidizing gas by electrochemical reaction; a hot water storage tank for hot water heated by heat generated when power is generated by the fuel cell power generating equipment; and an auxiliary water supply path for supplying auxiliary water to the hot water storage tank. The fuel cell power generating equipment has a fuel cell stack, a coolant circulation path for regulating a temperature of the fuel cell stack, a heat exchanger for condensing steam in an exhaust gas discharged from the fuel cell stack and recovering the condensed water, a water treatment system for purifying supply water recovered by the heat exchanger and supplying the purified supply water as coolant to the coolant circulation path, and heating means for heating water to provide hot water using the coolant. The heat exchanger condenses the steam in the exhaust gas by cooling the steam with the auxiliary water flowing in the auxiliary water supply path.
To operate the fuel cell power generating system, it is possible to employ a method which allows the heat exchanger to condense the steam in the exhaust gas by cooling the steam with the auxiliary water flowing in the auxiliary water supply path.
This structure can provide condensed water using auxiliary water having a lower temperature as compared with a fuel cell power generating system having a heat exchanger which condenses steam in the exhaust gas with coolant whose temperature becomes relatively high.
It is therefore possible to improve the efficiency of cooling steam in the exhaust gas to thereby increase the recovery amount of the condensed water or distilled water whose impurities, such as ions, are present in low concentrations. This can reduce a load of demineralization or the like applied to the water purifying equipment.
This allows setting the capacity of the water purifying equipment low, thus making it possible to reduce the equipment cost and the operation cost for the water purifying equipment, and decreases the space for this equipment.
As the recovery amount of condensed water can be increased, the cost needed for auxiliary water can be restrained further.